fix for DA-NRW 590. sidecar extension and file extension both automatically converted to lower case. case in extension is ignored.
Merge branch 'master' of https://github.com/da-nrw/DNSCore
refactor retrieval action and test for new feature of versioned retrieval
refactorings in preparation for work at retrieval action.
Merge branch 'master' of https://github.com/da-nrw/DNSCore